Upgrade to 2021 edition

[obeis]

Signed-off-by: Obei Sideg [email protected]

Summary of the PR

Upgrade to 2021 edition

Requirements

Before submitting your PR, please make sure you addressed the following
requirements:

• All commits in this PR are signed (with git commit -s), and the commit
  message has max 60 characters for the summary and max 75 characters for each
  description line.
• All added/changed functionality has a corresponding unit/integration
  test.
• Any newly added unsafe code is properly documented.

[jiangliu]

What's the benefits of this upgrading?

[obeis]

I think it's better to use latest stable version of rust

[wllenyj]

https://doc.rust-lang.org/edition-guide/editions/index.html#editions-do-not-split-the-ecosystem

The most important rule for editions is that crates in one edition can interoperate seamlessly with crates compiled in
other editions. This ensures that the decision to migrate to a newer edition is a "private one" that the crate can make
without affecting others.

Does this mean that other crates that depend on this crate will not fail to compile due to the editions issue?

[stefano-garzarella]

https://doc.rust-lang.org/edition-guide/editions/index.html#editions-do-not-split-the-ecosystem

The most important rule for editions is that crates in one edition can interoperate seamlessly with crates compiled in
other editions. This ensures that the decision to migrate to a newer edition is a "private one" that the crate can make
without affecting others.

Does this mean that other crates that depend on this crate will not fail to compile due to the editions issue?

So it looks like we can update it.

I think this PR fell into the crack, let's try to start again ;-)

@obeis can you rebase on current main?

[obeis]

@stefano-garzarella Done